Method and apparatus for treating sewage

ABSTRACT

Elimination of heavy solids such as grit from sewage streams prior to introduction into treatment tanks is necessary because such solids interfere with normal operations. Substantially all of the heavy solids, irrespective of particle size are removed by a process and apparatus wherein raw sewage is introduced into a tank, the preferred form of which has a bottom sloping downwardly from the far side to a trough adjacent a first side wall, with even distribution along said first side wall, a predetermined small range of liquid level variation is maintained by flowing effluent sewage over a weir extending above the full length of the top of the side wall opposite said first side wall, air is introduced with even distribution adjacent to said trough and along said first side wall to induce circulatory flow of liquid and light weight solids upwardly and then in the direction of said opposite side wall, turning the circulatory flow direction downwardly toward the tank floor by a baffle spaced from said opposite side wall and positioned transverse to the direction of liquid flow through said tank, to effect separation of light weight solids and flowing the sewage suspension under said baffle and upwardly for removal by flow over said weir.

United States Patent 1 1 Brociner 1451 Jan. 16, 1973 1541 METHOD ANDAPPARATUS F0 TREATING SEWAGE Haskal Brociner, Chicago, Ill.

Primary Examiner-John Adee Att0rneyDressler, Goldsmith, Clement & Gordon[57] ABSTRACT Elimination of heavy 5015s such as grit from sewagestreams prior to introduction into treatment tanks is necessary becausesuch solids interfere with normal operations. Substantially all of theheavy solids, ir-

zrespective of particle size are removed by a process and apparatuswherein raw sewage is introduced into a .tank, the preferred form ofwhich has a bottom slop- 4 'ing downwardly from the far side to a troughadjacent a first side wall, with even distribution along said first sidewall, a predetermined small range of liquid level variation ismaintained by flowing effluent sewage over a weir extending above thefull-length of the top of the side wall opposite said first side wall,airv is introduced with even distribution adjacent to said trough andalong said first side wall to induce circulatory flow of liquid andlight weight solids upwardly and then in the direction of said oppositeside wall, turning the circulatory flow direction downwardly toward thetank floor by a baffle spaced from said opposite side wall andpositioned transverse to the direction of liquid flow through saidtank,.to effect separation of light wcight solids and flowing the sewagesuspension under said bafflc and upwardly for removal by flow over saidweir.

5 Claims, 2 Drawing Figures PATENTEBJAN 16 I975 2 INVENTOR HA SKALBROC/A/ER ATTORNEYS METHOD AND APPARATUS FOR TREATING SEWAGE Thisinvention relates to a method and apparatus for treating sewage. Moreparticularly, it relates to a method and apparatus for separating from aflowing liquid stream grit and other sedimentary, abrasive matter, whichdoes not readily lend itself to the general methods of classification orsedimentation. Still more particularly, it is concerned with means forproducing a liquid sewage containing sewage solids to be subsequentlytreated, from a grit tank with substantially all grit removed therefrom.

Briefly, the method for removal of grit from sewage containingrelatively light organic matter, heavier but relatively small particlesof grit and relatively heavy particles of grit comprises the steps offlowing said influent sewage into said tank with a uniform distributionalong a first side wall positioned transverse to the direction of liquidflow, introducing air into said sewage with uniform distribution alongthe side wall supporting the inlet for influent sewage to createconditions which will cause heavy grit to settle out to an accumulationzone adjacent to and parallel to the side wall supporting said sewageinlet and to cause sewage still containing light organic matter andsmall particles of grit to flow upwardly and crosswise of said tank,positioning a baffle in said tank transverse to the direction of liquidflow therethrough and adjacent the side-wall topped by a liquid outlet,to intercept the liquid flow and to cause the flow to turn downwardlywhereby light grit is subjected to downward movement in addition togravity to cause it to deposit on the tank bottom, again reversing thedirection of flow of the sewage and the suspended light organic matterto an upwardly direction by passage under the baffle and flowingupwardly to an outlet supported by and extending the full length of saidside wall and removing grit solids from said accumulation zone.

The heavy solids in a sewage stream, such as grit, sand and gravel havebeen removed heretofore by means of grit chambers. The removal of sewagesolids from the grit tank depended upon the circulation of the sewageinduced by air forced into the sewage adjacent the sewage inlet of thetank. As disclosed in Morgan US. Pat. No. 2,532,457, the circulation ofthe liquid sewage serves to keep the organic matter and light gritparticles in suspension and separate from the heavy grit material. Theintroduction of gas in the Morgan apparatus which suspends light grit aswell as organic matter, creates the problem of light grit carrying intothe vicinity of an overflowing sewage outlet weir, thus lowering thegrit separation efficiency. As disclosed in Tapleshay U.S. Pat. No.3,297,567, the influent sewage is introduced through an inlet in alongitudinal side adjacent one end of the tank, air is introduced alonga portion of the longitudinal side of the tank in an area approachingthe outlet end of the tank and a baffle is positioned adjacent theoutlet end of the tank transverse to the direction of liquid flow, andparallel to the liquid circulation.

The turbulence created by the introduction of gas adjacent the baffleand the increased velocity of liquid flow in a spiral path adjacent thebaffle are counteractants to the gravity settling of solids in the zonebehind the baffle and result in the carryover of significant amounts oflight weight grit with the sewage suspension.

Now it has been discovered that inlet means spanning the full length ofand adjacent or near the top of one of the side walls, such as a weir, acontinuous port or a'multiplicity of ports, enables better flowdistribution and in conjunction with aeration means effects eliminationof any strong individual liquid streams flowing from the inlets andcarrying grit in the direction of the'outlet means and parallel liquidoutlet means results in lower head losses, more even washing, smallerfluctuation in water level and more even air flow with a new result ofeven grit distribution and substantially complete settling out of gritdue to a combination of gravity and downward flow of suspension in frontof and along the baffle caused by the break in the circulation patternby the baffle.

The method of removing substantially all the heavy solids from sewagecontaining relatively light organic matter and lightweight solids ofspecific gravity greater than that of said organic matter, i.e., heavierbut relatively small particles of grit and relatively heavy particles ofgrit comprises flowing said sewage into said tank whose floor terminatesin an accumulation zone for solids parallel to and adjacent a first sidewall with uniform distribution along said first side wall, said wallbeing positioned transverse to the direction of liquid flow in saidtank, introducing air into said'sewage at a predetermined pressureadjacent said first side wall with uniform distribution along the lengthof said first side wall in an amount'to induce liquid containing lightorganic matter and lightweight solids of specific gravity greater thansaid organic matter to flow upwardly initially and then toward a secondside wall opposite said first side wall while relatively heavy particlessettle directly to said accumulation zone, and when said flow approachessaid second side wall, interrupting the circulatory flow and directingit downwardly to the tank floor by a baffle positioned adjacent saidsecond side wall to effect separation of heavier but relatively smallparticles of grit, which tank floor preferably slopes downwardly fromthe point below the baffle toward said accumulation zone for solidspositioned below said area of introduction of air and parallel to andadjacent said first side wall from which zone accumulated solids can beindependently removed, flowing the sewage, minus the separated solids,under the baffle and upwardly between said baffle and said second sidewall for removal by flow over a weir extending the full length of saidsecond side wall and adapted to maintain a predetermined limitedvariation in liquid level in said tank.

The apparatus for effecting the grit separation, i.e., for removing gritand other particulate solids of relatively high specific gravity from aliquid containing same in suspension comprises a tank having a slopingbottom and a plurality of end and side walls, inlet means spanning thefull length of one of said side walls for uniform distribution ofinfluent suspension, a trough in said bottom extending completely alongsaid tank adjacent said side inlet wall, an overflow weir formaintaining a desired level of liquid in said tank extending the fulllength of an positioned at the top of the side wall opposite said inletwall, and an outlet for the liquid communicating therewith, means forintroducing air into the body of liquid from a region above said troughextending the full length of and adjacent said inlet wall to circulatethe liquid in a generally vertical plane in the direction of saidoverflow weir, and to wash heavy solids which settle out of said liquidalong said tank bottom sloping from said outlet wall to said trough,conveying means for removing solids from said trough, a baffle extendingcompletely along said tank parallel to said wall topped by said overflowweir having its upper edge extending above the maximum liquid level andits lower edge spaced adjacent said floor to provide an exit for liquidflow upwardly behind said baffle to said outlet, and a fillet withsurface extending downwardly from said side wall topped by said weir toa point below the lower edge of said baffle.

The structure by means of which the abovedescribed method of operationis carried out with the advantages attained, is described in thefollowing detailed description of a preferred form of apparatus for usein treating sewage in accordance with the instant invention, isillustrated in the accompanying drawings, in which:

FIG. 1 is a plan view of the tank; and

FlG.'2 is a cross section view along the line 2-2 of FIG. 1."

Referring to the drawings, the numeral indicates a tank of concrete orother suitable material. Tank 10 has a bottom 11, side walls 12 and 13and end walls 14 and 15. The bottom 11 of the tank has a fillet withsloping surface 16 of an angle of the order or about 45 from thehorizontal, extending from the wall 13 downwardly to a point below abaffle 17 which is spaced from wall 13 a distance providing a velocityof upward flow of sewage between it and wall 13 which will not carrywith it any appreciable quantity of light weight grit, at the liquidinflow volume of the sewage. Bottom 11 extends from the lowermost pointof surface 16 in a gentle slope downwardly to a trough 18 which extendsalong the tank bottom 11 parallel to side wall 12.

At the top of side wall 12, there is a diverging exten sion 20 whichextends interiorly of the tank. Wall 12 is also provided with aninfluent sewage channel 21 which extends along the entire lengththereof.

Extension 20 is adapted with ports 23 which are openings into the tank10 from the bottom of channel 21. Ports 23 are provided with adjustablegates 24 for control of flow of sewage into the tank.

Liquid in tank 10 is maintained at a substantially constant level, i.e.,with little level variation near the top of the tank as by the overflowweir 25 at the top of side wall 13. Liquid overflowing weir 25 isdirected to equipment for subsequent processing'of the sewage by outletchannel 26.

An air diffusing device, indicated generally by the numeral is placedwithin the tank with the air diffusion units 31, positioned adjacent toside wall 12 in a horizontal position with individual units extendingtransverse thereto, a short distance above the trough 18. The airdiffusing device may be of a stationary character but it is preferred touse devices which can be elevated out of the tank for servicing such asis described and claimed in the US. Pat. to Chase, No. 3,160,685, issuedDec. 8, 1964. The form of air diffuser unit illustrated in the drawingis of the Swing" type.

Air diffusion device 30 is conventional and need not be described indetail. The introduction of air into the sewage adjacent the side wall12 of the tank causes a circulatory movement of the sewage about ahorizontal axis parallel to wall 12 in a direction initially away fromand then back toward the air diffuser units. Grit and other heavy solidsin the liquid continuously settle along the sloping bottom of the tankand are swept by the liquid into the trough 18. As grit particles aremoved toward the trough 18, they are washed substantially free oforganic solid matter by the time they reach the trough.

A screw conveyor 32, positioned in the trough 18,

may be used to move the accumulated grit to an area from which it can beremoved by any suitable means. The screw conveyor may be omitted and thegrit removed in any suitable manner. 7

A baffle 17 extending parallel to the wall 13 has the lower end thereofspaced vertically from the lowermost end of sloping surface 16 and itsupper edge above the liquid level of the tank. The baffle extends allthe way from wall 14 to wall 15 and the only way any of the sewage canflow over the effluent weir 25 is through the space between the baffleand wall 13.

As raw sewage flows into the tank through inlet ports 23, an equalamount of sewage flows over the effluent weir and into the effluentchannel for delivery to other tanks for subsequent treatment.

Scum which may accumulate at the water surface of tank 10 may bedirected to the outlet channel 26 through ports 33 adjacent the top ofsaid baffle, said ports having a height adapted for passage of liquidwhatever the limited liquid level variation in the tank 10 and scumgates 34 are associated with said ports for control of movement ofscumtherethrough.

While one embodiment of the invention has been shown and describedherein, it will be understood that the description thereof is intendedto be illustrative, rather than restrictive, as many details ofstructure may. be modified or changed.

lclaim:

1. A method of removing grit from liquid sewage in a tank whose floorterminates in an accumulation zone for solids parallel to and adjacent afirst side wall, said sewage containing relatively light organic matter,heavier but relatively small particles of grit and relatively heavyparticles of grit, said method comprising flowing said sewage into saidtank with uniform distribution along said first side wall positionedtransverse to thedirection of liquid flow in said tank, introducing airinto said sewage adjacent said first side wall and above saidaccumulation zone for solids with uniform distribution along the lengthof said side wall in an amount to induce liquid containing light organicmatter and light particles of grit of specific gravity greater than saidorganic matter to flow upwardly initially and then toward a second sidewall opposite said first side wall, interrupting the circulator flow anddirecting it downwardly to the tank floor by a baffle positionedadjacent said second side wall and flowing the sewage under said baffleand upwardly between said baffle and said second side wall for removalby flow over a weir extending the full length of said second side wall.

2. A method according to claim 1 wherein said uniform distribution ofsewage in the tank is attained through ports spaced along said firstside wall and communicating with the channel extending the length ofsaid inlet wall.

3. A method according to claim 1 wherein scum accumulating at thesurface of liquid in said tank and moving in response to the circulatoryflow of liquid is directed to the outlet channel by flow through portsadjacent the top of said baffle, said ports being provided withadjustable closure means.

4. An apparatus for removing grit and other particulate solids ofrelatively high specific gravity from a liquid containing same insuspension comprising a tank having a sloping bottom and a plurality ofend and side walls, inlet means spanning the full length of one of saidside walls for uniform distribution of influent suspension, a trough insaid bottom extending completely along said tank adjacent said sideinlet wall, an overflow weir for maintaining a desired level of liquidin said tank extending the full length of and positioned at the top ofthe side wall opposite said inlet wall, and an outlet for the liquidcommunicating therewith, means for introducing air into the body ofliquid from a region above said trough extending the full length of andadjacent said inlet wall to circulate the liquid in a generally verticalplane in the direction of said overflow weir, and to wash heavy solidswhich settle out of said liquid along said tank bottom sloping from saidoutlet wall to said trough, conveying means for removing solids fromsaid trough, a baffle extending completely along said tank parallel tosaid wall topped by said overflow weir having its upper edge extendingabove the maximum liquid level and its lower edge spaced adjacent saidfloor to provide an exit for liquid flow upwardly behind said baffle tosaid outlet, and a fillet with surface extending downwardly from saidside wall topped by said weir to a point below the lower edge of saidbaffle.

5. Apparatus according to claim 4 wherein ports are provided adjacentthe top of said baffle, said ports having a heightadapted for passage ofliquid whatever the limited liquid level variation in said tank andgates associated with said ports for control of flow of scumtherethrough.

2. A method according to claim 1 wherein said uniform distribution ofsewage in the tank is attained through ports spaced along said firstside wall and communicating with the channel extending the length ofsaid inlet wall.
 3. A method according to claim 1 wherein scumaccumulating at the surface of liquid in said tank and moving inresponse to the circulatory flow of liquid is directed to the outletchannel by flow through ports adjacent the top of said baffle, saidports being provided with adjustable closure means.
 4. An apparatus forremoving grit and other particulate solids of relatively high specificgravity from a liquid containing same in suspension comprising a tankhaving a sloping bottom and a plurality of end and side walls, inletmeans spanning the full length of one of said side walls for uniformdistribution of influent suspension, a trough in said bottom extendingcompletely along Said tank adjacent said side inlet wall, an overflowweir for maintaining a desired level of liquid in said tank extendingthe full length of and positioned at the top of the side wall oppositesaid inlet wall, and an outlet for the liquid communicating therewith,means for introducing air into the body of liquid from a region abovesaid trough extending the full length of and adjacent said inlet wall tocirculate the liquid in a generally vertical plane in the direction ofsaid overflow weir, and to wash heavy solids which settle out of saidliquid along said tank bottom sloping from said outlet wall to saidtrough, conveying means for removing solids from said trough, a baffleextending completely along said tank parallel to said wall topped bysaid overflow weir having its upper edge extending above the maximumliquid level and its lower edge spaced adjacent said floor to provide anexit for liquid flow upwardly behind said baffle to said outlet, and afillet with surface extending downwardly from said side wall topped bysaid weir to a point below the lower edge of said baffle.
 5. Apparatusaccording to claim 4 wherein ports are provided adjacent the top of saidbaffle, said ports having a height adapted for passage of liquidwhatever the limited liquid level variation in said tank and gatesassociated with said ports for control of flow of scum therethrough.